This application relates to hydraulic devices of the type in which a series of expandable and contractable fluid pockets are defined between the intermeshing teeth of a gerotor gearset having an internally toothed stator and an externally toothed rotor adapted for relative orbital and rotational movement. It relates particularly to hydraulic devices of the type in which each internal tooth of the stator comprises a cylindrically shaped roller located in a recess of the stator, and which rollers rotate in their recesses and also perform a vaning function by engaging the teeth of the rotor to seal the high pressure zones of the device from the low pressure zones.
There are many known forms of hydraulic devices in which a series of expandable and contractable fluid pockets are formed between the intermeshing teeth of a gerotor gearset having an internally toothed stator whose teeth are formed by a series of cylindrical rollers located in recesses in the stator and which rotate and vane during operation of the device. The recesses and the cylindrical rollers are dimensioned such that the recesses provide rolling support for the rollers. U.S. Pat. No. 3,289,602 is typical of such devices.
The inner wall of the recesses and the outer walls of the rollers have smooth surface finishes and their dimensioning is such that a film of high pressure fluid is formed between them as the device operates. The film of high pressure fluid helps to seal the high pressure zone from the low pressure zone by applying a resultant force having a substantial radial component against the roller teeth of the stator to move and maintain rollers in sealing engagement with the rotor teeth. Also the forces on the roller cause the roller to shift circumferentially and provide a seal between the roller and the surface defining the recess in which the roller is located. This action of the roller is referred to as a vaning action. The film of high pressure fluid also serves to reduce wear between the rollers and stator by providing lubrication between the rollers and the stator.
It has been recognized that at high operating pressures there are high resultant non-radial forces exerted against the cylindrical rollers and that these resultant non-radial forces tend to destroy the film of high pressure fluid between the rollers and the wall of their respective recesses. This results in considerable direct contact between the rollers and the wall of their respective recesses. As a result wear and/or galling can occur. Further, rolling action of the roller may then cease, resulting in wear of the rotor teeth due to a rubbing contact with the roller.
There have been various suggestions for designing hydraulic devices of this type in a manner which serves to positively maintain high pressure fluid between the rollers and their recesses to promote the sealing action of the rollers and to help to reduce wear on the rollers and the recess walls. One such suggestion can be found in the disclosure of U.S. Pat. No. 3,915,603. In this patent each of the arcuate recesses is formed with a pair of additional recesses and each of the additional recesses receives a sealing member which is movable in the recess by pressures developed during operation of the device. The movement of the sealing member is intended to maintain a desired film of high pressure fluid between each roller member and its respective pocket. The sealing member operates as a seal and not as a load carrying member to carry the load of the roller.
Another type of suggested device is designed to direct fluid to the areas between the rollers and the arcuate recesses as shown in U.S. Pat. No. 3,692,439. According to the disclosure of this patent high pressure fluid is diverted directly to the area between the rollers and the recesses for forcing the rollers into engagement with the teeth of the rotor. In positively diverting high pressure fluid for this purpose this device apparently sacrifices some degree of volumetric efficiency.
In U.S. Pat. Nos. 3,915,603 and 3,692,439 while provision is made for maintaining fluid in the recesses to shift the roller radially, the galling due to circumferential movement of the rollers can occur. Further, these structures are somewhat complicated and expensive and require a multiplicity of parts.
A suggestion to minimize galling of the roller and the stator recesses is shown in U.S. Pat. No. 3,460,481 in which the inner wall of each recess is provided with a lining such as Teflon. Here again this is a somewhat complicated and expensive structure.